Integrated circuit chips are being used now in all kinds of apparatus to provide complex electrical circuitry for controlling different operations or for providing data and mathematical calculations in business, education, science and many other fields. With progressive advances in time, the size of the integrated circuit chips has progressively decreased. Even as the chips have decreased in size, the circuitry on the chips has become progressively complex.
The fabrication of each layer on an integrated circuit is provided by disposing a target, or targets, and the substrate in apparatus which includes an anode. The target(s) and the anode define a cavity. The electrical potentials on the target(s) and the anode cause an electrical field to be produced between the anode and the target(s) in a first direction in the cavity. A magnetic field is also produced in the cavity in a second direction transverse, and preferably substantially perpendicular, to the first direction.
The combination of the electrical and magnetic fields causes electrons in the cavity to move in a spiral path. These electrons ionize molecules of an inert gas (e.g. argon) which flow through the cavity. The ions are attracted to the target(s) and cause atoms to be emitted from the target(s). The atoms become deposited on the substrate to form a layer on the substrate. The layer may be an electrically conductive material or it may be a dielectric (or electrically insulating) material.
When the layer is formed from an electrically conductive material, the material is etched to form electrical leads. The integrated circuit chips are formed from a plurality of successive layers, some of which are electrically conductive and others of which are electrically insulating. Electrical pegs or vias are provided between the different electrically conductive layers. The electrical pegs or vias are disposed in sockets provided in insulating layers in the chips. The integrated chips are formed in wafers, each of which holds a plurality, sometimes hundreds and often even thousands, of integrated circuit chips.
The fabrication of the different layers in an integrated circuit has to be precise. For example, the thickness and width of the circuit leads in the different layers have to be precise in order to maintain the proper impedance values for different components in the circuits. If the proper impedance values are not maintained, the operation of the electrical circuitry in the integrated circuit chip is impaired. Sometimes two targets are disposed in the cavity. The targets are preferably made from the same materials but they may be made from different materials. The targets may be disposed in a co-axial (preferably frusto-conical) relationship. Material from each of the targets is deposited on the substrate to form a layer. The layer has different thicknesses at different positions on the substrate because each of the targets provides a different contribution to the substrate layer than the other target.
Gases existing in the cavity may be oxygen (O2), nitrogen (N2) and methane (CH4). These gases combine with atoms of the material forming the target(s) and produce compounds which settle on the targets and other members forming the deposition apparatus. For example, aluminum (Al) may combine with oxygen (O2) to form aluminum oxide (Al2O3); silicon (Si) may combine with nitrogen (N2) to form silicon nitride (Si3O4); silicon (Si) may combine with methane to form silicon carbide (SiC); and tantalum (Ta) may combine with oxygen (O2) and nitrogen (N2) to form (TaOxNy).
All of these resultant materials constitute solid dielectrics. When deposited on a member receiving a voltage, they prevent the member from receiving the benefit of the received voltage. For example, when one of these dielectric compounds is deposited on a target, it prevents an electrical field from being produced between the anode and the target, thereby preventing atoms of the material on the target from being emitted from the target.
When two (2) targets are disposed in the cavity, they receive an alternating voltage which causes one of the targets to be activated in alternate half cycles and the other one of the targets to be activated in the other half cycles. In this way, each target plays the role of an anode while the other target is activated. When activated, each target deposits atoms of the target material on the substrate and removes a thin dielectric material grown on its surface during the previous half cycle. Thus a self-cleaning process occurs. Every time that one of the targets is activated, it produces a voltage spike. This voltage spike prevents a smooth and uniform deposition of the target material from being provided on the substrate. A smooth and uniform deposition is desirable because it enhances the operation of the electrical circuitry formed on the substrate. Moreover, the spike creates particles and defects in the film deposited on the substrate.